The overall aims of this research are to understand the molecular mechanism by which muscle proteins convert chemical energy into mechanical work, and to obtain a precise correlation between the physiological and biochemical events of muscular contraction at the molecular level. Novel methods utilizing infrared optical traps (laser tweezers) will be applied capable of detecting mechanical events in individual myosin molecules and in individual interactions with filamentous actin. A new variant of the optical trap has been developed to effectively eliminate mechanical compliance in series with the measured contractile protein that normally obscures quantitative aspects of molecular events. Experiments are designed to probe the relations between biochemical reactions of the contractile proteins and the elementary mechanical steps of the cross-bridge cycle. Rapid changes in the chemical concentrations of pertinent biochemical species, such as ATP, will be made by laser pulse photolysis of photolabile "caged" precursors in the region of the interacting actomyosin. This method combined with the laser optical trap will resolve mechanical properties in various regions of the myosin molecule and the dependence of mechanical and biochemical reaction rates on mechanical strain imposed by sliding of the filament. The experiments will be carried out on single molecules of myosin from rabbit psoas muscle and on fragments of vertebrate myosin expressed in a heterologous expression system. Results from this project should significantly advance knowledge of the contractile process and thus bring a greater understanding of both normal and pathological states of striated muscle and other types of cell motility.